The present invention generally relates to a method and apparatus for a heat pump system, and more particularly to an electrochemical heat pump useful to compress and transfer a refrigerant.
Cooling of different devices utilizing a vapor compression refrigeration cycle is known in the art. Vapor compression cooling uses the thermodynamic principles associated with phase transfer, specifically the latent heal of vaporization and the entropy of evaporation of a working fluid. Compression of a vaporous working fluid can occur through mechanical or electrochemical means. Mechanical compression requires a relatively large, heavy, mechanical compressor having a great number of parts which are often bulky and susceptible to wear. After compression, the heated working fluid is condensed and gives up its latent heat of vaporization to a low temperature reservoir often referred to as a heat sink. The liquefied working fluid is then expanded at constant enthalpy. The cool liquefied working fluid can be used to exchange heat with a hot element by giving up its latent heat of vaporization. This cycle is known as a Joule-Thomson refrigeration cycle.
Electrochemical compressors have been proposed to drive Joule-Thomson refrigeration cycles, such as in U.S. Pat. No. 4,593,534 by Bloomfield, which is hereby incorporated by reference in its entirety herein. The cycle uses a working fluid, at least one component of which is electrochemically active as per that patent. Another component of the working fluid is condensable. In one embodiment, the electrochemically active component is hydrogen and the condensable component is water. The electrochemical compressor raises the pressure of the working fluid and delivers it to a condenser where the condensable component is precipitated by heat exchange with a sink fluid. The working fluid is then reduced in pressure in a thermal expansion valve. Subsequently, the low pressure working fluid is delivered to an evaporator where the condensed phase of the working fluid is boiled by heat exchange with a source fluid.
The major disadvantages of that approach are penetration of refrigerant (e.g., water) vapor in the electrode stack of the pump. Indeed, the electrode stack, which contains a series of connected electrochemical cells should have a small but certain amount of water. The excess water causes low pump activity because of diffusion resistance for hydrogen penetration. The lack of water results in high impedance of the membrane electrode assembly (MEA). If the working fluid shares a common gas space with the pump, the amount of water in the pump is excessive. The water in the MEA and the working fluid has non-stop vapor exchange through the common gas space. This may create pump flooding or drying.
U.S. Pat. No. 4,829,785 by Hersey describes a cryogenic cooling system using hydrogen as a primary refrigerant fluid and oxygen as a secondary refrigerant fluid to pre-cool the hydrogen gas below its inversion temperature. The hydrogen and oxygen are cooled through the Joule-Thomson effect of adiabatic gas expansion. After the refrigeration cycle is completed, the hydrogen and oxygen electrochemically react to create water. The problems with this approach may include the small Joule-Thomson effect associated with the hydrogen and the necessity to burn the hydrogen and oxygen to water in an exothermic reaction (producing additional heat).
Also, as described in U.S. Pat. No. 4,523,635 by Nishizaki et al., which is hereby incorporated by reference in its entirety herein, it is known that certain metals and alloys exothermically occlude hydrogen to form a metal hydride. The metal hydride reversibly releases hydrogen. A heat pump (e.g., a refrigerator) may be constructed by providing a first metal-hydride (M1H) and a second metal-hydride (M2H), which have different equilibrium dissociation pressures at the same temperature, in closed receptacles capable of effecting heat exchange with a heat medium, and connecting these receptacles with a common gas space conduit so as to permit the transfer of hydrogen there between.
However, these types of heat exchange devices rely on differences in equilibrium dissociation pressures of the respective metal hydrides. The metal hydrides utilized must be able to occlude and release hydrogen at very substantial rates, and metal hydrides of this type are very expensive to manufacture and utilize. Additionally, it is difficult to efficiently control the production and consumption of hydrogen during operation of the heat exchanger using principles of dissociation of hydrogen from metal hydrides.
Also, as described in U.S. Pat. No. 5,746,064 and U.S. Pat. No. 5,768,906, which are both owned by Applicant and hereby incorporated by reference in their entireties herein, it is known that an electrochemical pump based on electrochemical cells can be used in a heat exchange system.
In addition, as described in U.S. application Ser. No. 09/353,458, which is owned by Applicant and hereby incorporated by reference in its entirety herein, an electrochemical hydrogen pump has been proposed for use in a number of heat exchange applications. The electrochemical heat exchanger includes a housing, hydrogen producing/consuming portions separated by a proton exchange membrane, and a gas space designed to contact an object to be cooled. The gas space includes either hydrogen or a liquid gas that is placed in thermal contact with an item to be cooled. The hydrogen gas or liquid coolant exchanges heat with the object to be cooled and is constantly replenished by hydrogen or liquid coolant forced through the heat exchanger by a pressure differential created between the respective hydrogen electrodes.
In accordance with the present invention, there is provided an electrochemical heat pump for use in a vapor refrigeration cycle that includes a hydrogen electrochemical pump, a chamber divided by a flexible separator into a gas space and a refrigeration space, and a refrigerant-based cooling system. Preferably, the hydrogen electrochemical pump is capable of producing hydrogen gas at a hydrogen electrode and consuming hydrogen gas at a first electrode thereby creating a pressure differential between the two electrodes. As hydrogen gas is produced, the hydrogen gas enters the first gas space and expands the flexible separator.
Preferably, two chambers are utilized wherein the first chamber is divided by a first flexible separator into a first gas space and a first refrigeration space, and the second chamber is divided by a second flexible separator into a second gas space and a second refrigerant space. The two chambers allow for production of hydrogen gas in the first gas space and consumption of the hydrogen gas in the second gas space.
Preferably, the flexible separators located between the gas space and the refrigerant space mechanically isolate the contents of the two spaces while keeping the contents of the two spaces in pressure contact with each other. Pressure contact is intended to mean that a pressure on one side of the separator from the contents of one of the systems will result in a deforming of the separator and a resultant increase in pressure and decrease in volume on the contents of the other system at the other side of the separator. The flexible separator used in the present invention may include a flexible diaphragm, bellow, or other device that may be used as a separator.
Preferably, the polarity of the hydrogen electrochemical pump is reversed upon receiving an input signal to create a reciprocal pump. The corresponding signal for polarity reversal may include a certain time period, a pressure differential between both sides of the separator, or a predetermined pump voltage. The polarity reversal causes a reduction reaction to take place at the first electrode of the hydrogen pump. As such reduction reaction occurs, hydrogen gas is produced at the first electrode and this hydrogen gas fills the second gas space causing the second flexible separator to expand. This completes one full cycle of the hydrogen pump.
In one embodiment, the refrigerant-based cooling system includes a first and second condenser, a first and second throttle valve, and an evaporator. As hydrogen gas is produced in the first gas space, the flexible separator expands, compresses the refrigerant stored in the refrigerant space, and forces the refrigerant through the first condenser to liquefy the refrigerant. The liquid then passes through the first throttle valve to reduce the pressure of the liquid refrigerant. The liquid refrigerant then passes through the evaporator to evaporate the liquid refrigerant by absorbing heat from an object to be cooled as latent heat of evaporation. Finally, the vapor refrigerant is pulled into the second refrigerant space. When the polarity is reversed, hydrogen gas is being produced in the second gas space causing the flexible separator to expand. When the flexible separator expands, it compresses the refrigerant stored in the second refrigerant space and forces it through the second condenser to liquefy the refrigerant. The liquid then passes through the second throttle valve to reduce the pressure of the liquid refrigerant. The liquid refrigerant then passes through the same evaporator to evaporate the liquid refrigerant by absorbing heat from an object to be cooled as latent heat of evaporation. Finally, the vapor refrigerant is pulled into the second refrigerant space. This completes one full cycle of the system.
In the preferred embodiment, the refrigerant-based cooling system includes a condenser, a throttle valve, an evaporator, and four one-directional valves used to direct the flow of the refrigerant. As hydrogen gas is produced in the first gas space, the flexible separator expands, compresses the refrigerant stored in the refrigerant space, and forces the refrigerant through the first one-directional valve and into the condenser to liquefy the refrigerant. The liquid then passes through the throttle valve to reduce the pressure of the liquid refrigerant. The liquid refrigerant then passes through the evaporator to evaporate the liquid refrigerant by absorbing heat from an object to be cooled as latent heat of evaporation. Finally, the vapor refrigerant passes through the second one-directional valve raid is pulled into the second refrigerant space. When the polarity is reversed, hydrogen gas is being produced in the second gas space causing the flexible separator to expand. When the flexible separator expands, it compresses the refrigerant stored in the second refrigerant space and forces it through the third one-directional valve and back into the condenser to liquefy the refrigerant. The liquid then passes through the throttle valve to reduce the pressure of the liquid refrigerant. The liquid refrigerant then passes through the evaporator to evaporate the liquid refrigerant by absorbing heat from an object to be cooled as latent heat of evaporation. Finally, the vapor refrigerant passes through the fourth one-directional valve and is pulled into the first refrigerant space. This completes one full cycle of the system.